<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        p:first-letter{
            color: red;
        }
        p:first-line{
            font-size: 20px;
            font-weight: bold;
        }

        div:before{
            content: "hello";
            color: green;
        }
        div:after{
            content: "world";
            color: red;
        }
    </style>
</head>
<body>
    <p>
        welcome to css
        <br>
        happy 520
    </p>

    <div>哈哈</div>
</body>
</html>